Add flour, salt, and sugar in a large bowl and mix. Add 12 TBSP butter and blend using a pastry blender until a pea-sized mixture forms.
While continuing to blend, pour the ice water in about 1 TBSP at a time, until the dough starts to come together. I do end up using the entire 1/2 cup, but am cautious while adding in case the dough comes together without all of the water.
Once dough comes together, transfer it onto a lightly floured surface and knead quickly into a ball, being careful not to overwork the dough. Form into a round disk and wrap in a sustainable wrap or plastic wrap, and refrigerate for at least 30 minutes.
TART ASSEMBLY:
While the dough chills, preheat the oven to 400°F and line a large jelly roll or sheet pan with parchment paper. Slice the peaches into about 1/4 inch thick slices (you want them fairly thin), removing the pit.
Once chilled, place the dough on a lightly floured surface. Roll the dough into approximately at 12 inch circle. Transfer the rolled dough onto your prepared baking sheet. Melt the remaining 1/2 TBSP butter and brush on the top of the dough. Layer the peach slices on top of the dough in rows, leaving approximately 1 1/2 - 2 inches around the edges to fold up. Once your peaches are placed, fold up the sides - this does not have to be perfect! Brush the edges with the egg wash and sprinkle on the raw sugar as desired.
Bake the galette for 35-40 minutes until the pastry begins to brown.
When the galette is done baking, stir together the apricot preserves and water to thin it out a little. Brush the preserves on the peaches using a pastry brush.
Allow the galette to cool slightly; serve warm or at room temperature.
Notes
You can make the pastry dough using a food processor. Follow the steps as described above: pulse until flour, salt, sugar, and butter until butter is in small pea sized bits. Slowly pour in ice water while processor is running until dough is just combined.Store at room temperature or in the fridge; best eaten within 1-2 days.When assembling the tart, I do not use the end slices of the peach in order to have a uniform look.Leave off the egg wash for any egg allergies.